I'm not sure..but apparently the character was once called Beregond (they changed this because they felt it wasn't worth giving him that name, given how small his role had to be in the end), so I assume that they would have shot a few other scenes with the character, though I doubt he was ever intended to be a particularly notable presence.

Maybe he disapproved of Denethor's madness and went to join the battle below? Or possibly he tried to find Gandalf in order to warn him but ultimately got lost/couldn't find him/was killed, which meant that Pippin warned Gandalf when he found him later on. "These are Gundabad Wargs! They will outrun you!"

Iorlas of Gondor was the uncle of Bergil (in the book). Is this the same character? 'There are older and fouler things than Orcs in the deep places of the world.' - Gandalf the Grey, The Fellowship of the Ring

Seems like nobody has a clue. I was just wondering, seeing that Grimbold was supposed to have died during the Pelennor battle, that somebody, perhaps the actor himself or PJ, might have said something during a Q&A.